Drum brake assembly

ABSTRACT

In a brake assembly having a support member and a floating brake shoe provided with a web slidably mounted between oppositely facing guide ledges fixed to the support member for radial movement of the shoe into frictional engagement with a rotating drum. A preloaded shoe hold down spring is interposed between one of the ledges and the shoe web to urge the web against the other oppositely facing ledge so that the brake shoe is centrally positioned with respect to the drum and held out of contact therewith during brake release.

nited vStates Patent 1191 I Keller, 31'.

[ Mar. 5, i974 l l DRUM BRAKE ASSEMBLY [75] Inventor: Clarence Keller,Jr., South Bend,

Ind.

[73] Assignee: The Bendix Corporation, South Bend, Ind.

221 Filed: Feb.'l2, 1973 1211 Appl. 1901331912 [52] U.S.Cl...... 188/340511 1111.01. Fl6d 69/04 [58] Field of Search 188/340, 335, 326, 78

[56] References Cited UNITED STATES PATENTS 2,211,439 8/1940Schnclletal. ..188/340 2,263,949 11/1941 Harle 188/340 2,828,834 4 1958Smith 188 78 3,186,519

6/1965 .lohannesen ..188/340 Primary ExaminerDuane A. Reger AssistantExaminer-Charles E. Frankfort Attorney, Agent, or FirmKen C. Decker;William N. Antonis 57 ABSTRACT In a brake assembly having a supportmember and a floating brake shoe provided with a web slidably mountedbetween oppositely facing guide ledges fixed t0 the support member forradial movement of the shoe into frictional engagement with a rotatingdrum. A preloaded shoe hold down spring is interposed between one of theledges and the shoe web to urge the web against the other oppositelyfacing ledge so that thebrake shoe iscentrally positioned with respectto the drum and held out of contact therewith during brake release.

7 Claims; 5 Drawing Figures a i DRUM BRAKE ASSEMBLY BACKGROUND OF THEINVENTION The invention relates to automotive vehicle drum brakes andparticularly to wedge brakes commonly used on heavy duty vehiclesincluding trucks, trucktractors, trailers and semi-trailers.

A brake of the wedge actuated type is shown in US. Pat. No. 3,362,506wherein brake actuators, integrally mounted on the brake support member,are drivably connected to a pneumatically powered device through a wedgemechanism for moving the brake shoes into frictional engagement with thedrum. This brake I is commonly referred to as a floating shoe brakesince the two ends of the shoe are slidably carried on the actuatorpistons so that the shoe has free sliding chordal movement with respectto the drum surface to adjust concentrically thereto. The shoes are heldon the pistons by shoe return springs attached at opposite ends to therespective shoe webs. Due to the weight and size of such brakes, it hasbeen found from experience that brake shoe wear caused byvehiclevibration shifting the shoes against the rotatingdrum isminimized when the brake is mounted on a vehicle axle so that the shoesare horizontally disposed. Although horizontal mounting of the brakeshoes is preferable and produces optimum brake shoe lining wear pattern,such mounting is seldom achieved due to'interference between the servicebrake air chamber of the brake actuator and'the vehicle structure, themost common of which is the vehicle springs. The interference problemhas been resolved by indexing or rotating the brake assembly about thevehicle axle so that the service brake air chamber, for example, avoidsthe vehicle spring. However, indexing the brake so that the shoes are nolonger horizontally positioned introduces shoe wear into the shoes. Thisshoe end wear results from the fact that the shoes are slidingly orfloatingly carried on the pistons and are free to slideor shift into thedrum against the force of the return springs. This sliding action of theshoe ends into the drum, caused principally by vehicle vibration, isaggravated by rough roads and reduced return spring force, the latterdue to excessive use, overheating, etc. Therefore, such brakesrequireconstant vigilance to insure effective braking; The present in ventionis concerned with solving the brake shoe wear problem which heretoforeplagued the floating shoe brake.

- SUMMARY OF THE INVENTION A spring brake shoe hold down device. forinstallation in a floating shoe type of drum brake in the field toprevent the shoes from undesirable shifting into engagement with thedrum.

A spring brake shoe hold down device for a floating shoe type drum brakeis prestressed between a shoe support member, which. has a guide ledgeon which a brake shoe is radially slidably carried, and the web of theshoe so that the web is urged against the guide ledge with sufficientforce to hold the shoe fromundesirable shifting against the drumwhen-the brake is indexed off horizontal.

' A U-shaped shoe hold down spring insertable into a floating shoe typeof drum brake in the field without disassembly of the brake to hold theshoe from shifting into the drum due to vibration and road shock onbrakes that are indexed off horizontal.

DESCRIPTION or THE DRAWINGS FIG. 1 is a vertical section of a brakeassembly taken just inside the brake drum head, and embodying theprinciples .of my invention;

FIG. 2 is a schematic representation of a brake assembly of the typeshown in FIG. I, indexed off hori zontal and without the benefit of myinvention to illustrate brake lining wear;

FIG. 3 is a section through the brake of FIG. I on line 3-3;

FIG. 4 is a section taken on the line 4-4 of FIG. I; and v FIG. 5 is aprespective view of a brake shoe hold down spring according to myinvention.

DETAIL DESCRIPTION Referring now to FIG. I, the brake assembly withwhich the device of my invention is associated includes a support memberor torque spider 10, having an inner flange portion 12 with a pluralityof circumferentially spaced holes 14 for receiving mounting bolts, notshown, for fastening the spider to a vehicle axle flange, not shown.Guide pads or ledges l6 and 17, spaced apart axially, are diametricallylocated at the outer periphery of the spider for slidably supportingbrake shoes 18 and 20 provided with friction linings 22 and 24respectively. Actuators 26 and 28, having diametrically disposedhousings 30 and 32 respectively, are located between each pair ofadjacent ends of shoes I8 and 20. The housings 30 and 32 are integralwith the brake support 10 and each housing slidably receives identicalplungers or pistons 34 and 36, for sliding movement in a planetransverse to the brake axis for spreading the shoes 18 and 20 intofrictional engagement with a rotatable drum 38. The piston 36 includesan adjuster 40 for maintaining proper clearances between the linings 22and 24 and the drum 38. The automatic adjuster 40 associated with thepiston 36 is preferably of the type disclosed in US. Pat. No. 3,232,392to which reference is made for additional details of construction andoperation. Shoe return springs 42 interconnect webs 44 and 46 ofadjacent ends of the shoes 18 and 20 respectively, for urging their endsagainst their associated pistons. The shoe webs 44 and 46 have theirends slidingly positioned or floatingly carried on the pistons 34 and 36to permit chordal or transverse movement of the shoes within the drum soas to adjust to conform to the inner drum surface. The pistons 34 and 36of the actuators 30 and 32 are operatively connected to service brakeair chambers 48 and 50 through wedge assemblies, not shown, of any wellknown type such as disclosed in US. Pat. No. 3,362,506, assigned to thecommon assignee of this invention and incorporated herein by referencefor a more complete dissertation on wedge actuated brakes.

Mounting the brake assembly so that the shoes 18 and 20 are horizontallydisposed as shown in FIG, I is not always practical even thoughpreferable because of interference encountered between the pneumaticpower chambers 48 and 50 and the vehicle undercarriage including thesprings, not shown. To avoid this interference problem the brakeassembly is indexed or rotated so that the shoes are off horizontal asshown in FIG. 2. Although indexing the brake assembly avoids theinterfering vehicle structure, it has been found to be a majorcontributing factor to excessive shoe-end wear of the linings as can beseen with reference to areas 52 and 54 of the linings 22 and 24, of FIG.2. Indexing the brake assembly inclines the shoe ends on theirrespective pistons so that any jolting or shaking of the vehicle causesthe shoes to slide into engagement with the drum 38. This sliding actionof the shoe ends on their respective pistons becomes more acute as theshoe return springs 42 lose their force and resiliency.

The foregoing brief description of the brake assembly of FIG. I is thatof a floating shoe wedge activated brake, well known in the brake art.The brake will now be further described with respect to the improvementincorporated therein to differentiate it from prior brakes, such as thebrake assembly of FIG. 2.

In the improved brake, the shoes 18 and 20 are retained concentricallyof the drum 38 by a generally U- shaped shoe hold down spring 58prestressed between the spider 10 and shoes. The shoe hold down device58 is shown in FIG. apart from of spring steel. The U-shaped hold downdevice is constructed with a base portion 60 and two spaced-apartidentical legs 62 projecting from the base in a generally verticaldirection. Each leg is formed as an open-ended wire loop, having one endor side portion 64 of the loop attached to the base 60 and a free end orside'portion 66 flexibly supported as an integral part of the loop. Theends 64 and 66 of each loop are joined or closed at 67. Each free end 66is provided with a spring projection or finger 68 extending inwardlytoward the center of the space formed between the spaced-apart legs 62.The fingers 68 are oppositely disposed with their ends in facingrelationship to each other and terminating short of contact, in order toform a space 70 between the fingers 68 so that the device 58 can bereadily attached to a brake assembly in the field.

As illustrated in FIG. I, the shoe hold down device 58 is assembled onthe brake with the base 60 supported on an outer rim 72 of the spider10. The legs 62 straddle the ledge 17 so that the base 60 engages theunderside 74 of the ledge 17, securing the device from outward radialmovement, as best shown in FIGS. 3 and 4. The free ends 66 of the legs62 overlay the web and are stressed inwardly during assembly, as viewedin FIG. I, so that the fingers 68 engage the inner side 76 of the ledge17, as shown in FIG. 4. Stressing the ends 66, as aforementioned, so asto cause the fingers or projections 68 to engage the inner side of ledge17 rotates the closed ends 67 of the legs 62 against the web 44, asviewed in FIGS. 3 and 4, urging the web.into contact with the ledge 16.

The invention provides an improved one-piece brake shoe hold down spring58 having the advantage of field installation without disassembling thebrake to correct shoe end wear on floating shoe drum brakes. The device58 is merely interposed or prestressed between the the brake assembly ofFIG. 1 and is formed from a wire element, preferablysupport member 10and the brake shoe 18 so that the base is supported on the spider andthe fingers 68 engage the inner side 76 of the ledge 17, which rotatesthe legs 62 against the web 44 to thereby preload the shoe againstsliding into the drum due to vehicle vibration.

I claim:

1 In a brake assembly having a .torque spider with oppositely facingledges located at the outer periphery thereof and spaced-apart axiallyfor receiving a shoe web of an associated brake shoe floatinglysupported on its ends and an actuator for moving the shoe intoengagement with a rotating drum, the improvement for retaining the shoeconcentrically of the drum, said improvement comprising:

a shoe hold down device having a base supported on the spider arid twospacedapart legs projecting from the base in overlaying relationship tothe shoe web, and a spring finger carried by each leg urged intoengagement with one of the ledges so that the legs are prestressedagainst the web, forcing the web against the other of the oppositelyfacing ledges to thereby retain the shoe concentrically.

2. The improvement in claim 1 wherein the one ledge is formed with aninner side with which the fingers are engaged and an underside on whichthe base abuts to position the device with respect to the shoe.

3. The improvement in claim 2 wherein each leg is an open-ended wireloop. having a closed end abutting the web and an open end with twosides connected respectively to the base and to its related finger.

4. The improvement in claim 3 wherein the sides forming each loop aresubstantially parallel, one side being integral with the base andflexible with respect thereto, and the other side being freely flexibleabout the closed end of the loop.

5. An improved one-piece brake shoe hold down spring adapted to beinserted between a brake shoe and a brake support member, wherein theimprovement comprises:

a wire formed with a base from which two spacedapart legs in the form ofloops extend, each loop having a pair of sides joined at one end andopen at the other end with one side of the open end of the loop attachedto the base and the other side freely flexible to be prestressed whenattached to a brake.

6. The improvement in claim 5 wherein the joined end of each loop isintegral with said one side of the open end of the loop and rotatablyflexible about the base.

7. The improvement in claim 6 wherein said other side of each loop has afinger extending therefrom toward the other finger and terminating shortof engagement with one another to provide a space between said fingersto facilitate insertion.

1. In a brake assembly having a torque spider with oppositely facingledges located at the outer periphery thereof and spacedapart axiallyfor receiving a shoe web of an associated brake shoe floatinglysupported on its ends and an actuator for moving the shoe intoengagement with a rotating drum, the improvement for retaining the shoeconcentrically of the drum, said improvement comprising: a shoe holddown device having a base supported on the spider and two spaced-apartlegs projecting from the base in overlaying relationship to the shoeweb, and a spring finger carried by each leg urged into engagement withone of the ledges so that the legs are prestressed against the web,forcing the web against the other of the oppositely facing ledges tothereby retain the shoe concentrically.
 2. The improvement in claim 1wherein the one ledge is formed with an inner side with which thefingers are engaged and an underside on which the base abuts to positionthe device with respect to the shoe.
 3. The improvement in claim 2wherein each leg is an open-ended wire loop having a closed end abuttingthe web and an open end with two sides connected respectively to thebase and to its related finger.
 4. The improvement in claim 3 whereinthe sides forming each loop are substantially parallel, one side beingintegral with the base and flexible with respect thereto, and the otherside being freely flexible about the closed end of the loop.
 5. Animproved one-piece brake shoe hold down spring adapted to be insertedbetween a brake shoe and a brake support member, wherein the improvementcomprises: a wire formed with a base from which two spaced-apart legs inthe form of loops extend, each loop having a pair of sides joined at oneend and open at the other end with one side of the open end of the loopattached to the base and the other side freely flexible to beprestressed when attached to a brake.
 6. The improvement in claim 5wherein the joined end of each loop is integral with said one side ofthe open end of the loop and rotatably flexible about the base.
 7. Theimprovement in claim 6 wherein said other side of each loop has a fingerextending therefrom toward the other finger and terminating short ofengagement with one another to provide a space between said fingers tofacilitate insertion.